1. Field of the Invention
The present invention relates to novel optically active compounds each containing a naphthalene skeleton and to liquid crystal compositions containing these compounds.
2. Description of the Prior Art
Presently, various kinds of liquid crystal display devices are used in many fields because the display operation of these elements is advantageously possible at a low voltage, in a low consumption of electric power and in a thin form and because they are photoreceptive and therefore conveniently they do not cause eyes of operators to get tired.
Above all, TN (twisted nematic) type display systems each employing a nematic liquid crystal are utilized in an extensive range. However, these display systems have the drawback that a response speed is low.
The advancement of the recent industrial technology strongly requires a rapid responsivity even in the field of the liquid crystal devices, and in reply to such a requirement, many attemps have been made by improving materials for the liquid crystals. As one example which can meet the above-mentioned demand, a display device has been already suggested in which a photoswitching phenomenon of a ferroelectric liquid crystal is utilized [Appl. Phys. Lett., 36, 899 (1980)]. As a liquid crystal phase for the ferroelectric liquid crystal, a chiral smectic C (SC*) phase is practically desirable, and some of the liquid crystal compounds showing the chiral smectic C phase have been heretofore investigated. Typical examples of these liquid crystal compounds are set forth in Table 1.
With regard to the ferroelectric liquid crystal compounds each having a naphthalene skeleton, Japanese Patent Laid-Open Publication No. 248,790/1985 suggests the possibility of the presence of their compounds but does not refer to concrete examples of such compounds. In this technical field, it cannot be presumed at all at present what skeleton in the compound causes the ferroelectric properties in the liquid crystal and what physical properties the ferroelectric liquid crystal has. The inventors of the present application have found that liquid crystal compounds each having the naphthalene skeleton show remarkably excellent characteristics to compounds exemplified in the aforesaid patent publication, and the present invention has been completed on the basis of the found knowledge.
The conventional compounds in Table 1 may isomerize in a short period of time by light and may hydrolyze due to existent water, so that they come to have no liquid crystal phase any more at times. The compounds having such unstable factors are practically unpreferable as materials for various optical elements of displays and the like.
TABLE 1 __________________________________________________________________________ Chemical Structure Phase Transition __________________________________________________________________________ ##STR3## ##STR4## ##STR5## ##STR6## ##STR7## ##STR8## __________________________________________________________________________ The compounds 1 and 2 above are described in J. Physique, 37, C3129 (1976). The compound 3 is described in Mol. Cryst. Liq. Cryst. Letters, 82, 61 (1982).